Seismic vulnerability of skew bridges under bi-directional ground motions

• A systematic investigation has been conducted to assess the seismic vulnerability of bridges with varying skew angles.
• A suite of bi-directional ground motions representing different hazard levels has been considered.
• Vulnerability assessment has been done in terms of fragility curves for column and deck unseating damages.
• Effect of bridge skew angle and ground motion directionality on bridge responses and vulnerability has been studied.
• A PGA related better intensity measure is proposed that reduces the dispersion of fragility curves.

Past earthquakes have demonstrated that skew bridges are more vulnerable to earthquake induced failure than a normal bridge due to their complex load transfer mechanism. This study deals with the effect of skew angle on seismic vulnerability of these bridges under horizontal two-component (bi-directional) ground motions. For this purpose, representative models of two-span simply supported, typical highway overpasses with varying skew angles have been considered. Finite element models of these bridges, which have been designed using modern seismic provisions, are developed using a widely used software. A suite of bi-directional ground motions with varying strong motion properties and representing different hazard levels is used for nonlinear dynamic analysis and subsequent seismic vulnerability estimation using fragility curves. Deck unseating and damage of columns are considered as the damage measures for the vulnerability analysis. The effect of ground motion directionality on the vulnerability of bridges has also been investigated in this study. Results of this study indicate that as the skew angle increases, there is an increase in the probability of failure for a given ground motion intensity. It is also found that the dispersion of fragility curves for bi-directional ground motions can be minimized by using the square root of sum of squares (SRSS) of peak ground acceleration (PGA) of all components than the PGA of any component.